linux-kernel - Re: [PATCH] tracing: Decrement trace_array when bootconfig creates an instance

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Date:   Fri, 24 Jan 2020 21:25:31 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Divya Indi <divya.indi@...cle.com>
Subject: Re: [PATCH] tracing: Decrement trace_array when bootconfig creates
 an instance

On Sat, 25 Jan 2020 11:23:00 +0900
Masami Hiramatsu <mhiramat@...nel.org> wrote:

> On Fri, 24 Jan 2020 20:59:27 -0500
> Steven Rostedt <rostedt@...dmis.org> wrote:
> 
> > 
> > From: "Steven Rostedt (VMware)" <rostedt@...dmis.org>
> > 
> > The trace_array_get_by_name() creates a ftrace instance and
> > trace_array_put() is used to remove the reference. Even though the
> > trace_array_get_by_name() creates the instance, it also adds a reference
> > count to it, that prevents user space from removing it.
> > 
> > As the bootconfig just creates the instance on boot up, it should still be
> > used where it can be deleted by user space after boot. A trace_array_put()
> > is required to let that happen. Otherwise, the created instance can not
> > be removed.
> > 
> > Also, change the documentation on trace_array_get_by_name() to make this not
> > be so confusing.  
> 
> Good catch! I misunderstood trace_array_put() would remove the instance.

I figured as much, which is why I included the documentation update.

> 
> Acked-by: Masami Hiramatsu <mhiramat@...nel.org>

Thanks!

-- Steve